An Update to the Understanding of Nitric Oxide Metabolism in Plants

Abstract

Nitric oxide (NO) is an inorganic free radical gaseous molecule which has been shown to play an unprecedented range of roles in biological systems. The potential reactions of NO are numerous and depend on many different factors. The site and source of production, as well as the concentration of NO collectively determine whether NO will elicit direct or indirect effects. In animals, NO is generated by the activity of NOS (nitric oxide synthases). In plants, neither the gene nor protein similar to known NOS, have been found. However, different pathways producing NO in plants have been described, and can be classified as either oxidative or reductive steps. These sources of NO, seem to cooperate to the growth and development, and to respond to several stress situations like abiotic stress. Chloroplasts are key organelles in plant metabolism and they seem to be involved in NO production, thus, proposed pathways for NO generation in chloroplasts are discussed.